1. Field of the Invention
The present invention relates to the improved recovery of a print head in a printing device for maintaining the print head in a good printing condition. More specifically, the present invention relates to an improved recovery of a print head in an ink jet printing device wherein the improved recovery includes accurate positioning of the print head during recovery operations, protection of the caps and wiper during non-use, concurrent prefiring and wiping operations, dampened print head capping, and improved wiping with a partitioned, multi-portion wiper blade.
2. Description of the Related Art
A printing device, such as an ink jet printer, prints images onto a printing medium, such as paper or other sheet of material, by scanning a carriage carrying a print head across the printing medium while ejecting ink from the print head. Specifically, the carriage is scanned in a main scanning direction which crosses the printing medium perpendicular to the conveying direction, which is the sub-scanning direction. As the carriage is moved in the main scanning direction across the printing medium, the print head ejects ink to produce an image portion corresponding to one line. After completion of the image portion corresponding to the one line, the printing medium is conveyed by a predetermined amount in the sub-scanning direction, after which the image portion corresponding to the next line is printed. These operations are repeated until the entire image is printed on the printing medium.
Such an ink jet printing device is advantageous because the device can be designed and built in a small size, and because it is possible to print a high-resolution image at a high speed on ordinary paper at a low running cost. In addition, such an ink jet printing device can enable the printing of a color image by using inks of different colors in the print head, or in multiple print heads, mounted on the carriage. Different combinations of ink can be utilized to achieve desired color images and resolutions. For example, multiple print heads using only black ink can be utilized for printing of text, and multiple print heads wherein one print head uses black ink and another print head uses a color ink can be utilized to create color images. Different types of ink may also be used for desired results. For example, the black and color inks may be made dye ink or pigment ink.
In addition, reaction inks may be used to accomplish quick fixing of the ink on the printing medium as it is ejected from the print heads. For example, one print head may be utilized to eject a black ink which is anionic (carrying a positive charge) and another print head may be utilized to eject a color ink which is cationic (carrying a negative charge), whereupon the inks react with the printing medium and/or each other so that they are quickly fixed on the printing medium. In this manner, reaction inks can be used to prevent bleeding between black and color inks on the printing medium, and thereby achieve a desired resolution color image.
Typically, several ink discharge nozzles are located in the discharge surface of the print head for ejecting ink from the print head onto the printing medium. It can be appreciated that the discharge surface and the discharge nozzles can become contaminated with residuary ink that does not reach the printing medium. For example, during ejection of ink from the discharge nozzles, a fine mist of ink particles may exist in the ink jet printing device which may then adhere to the discharge surface of the print head.
In addition, paper powder, dust and other contaminants may inadvertently adhere to the discharge surface of the print head. Such contaminants can impair the ability of the discharge nozzles to properly eject ink onto the recording medium, and can thereby impair the quality of a recorded image on the printing medium and the overall efficiency of the ink jet printing device. This is particularly a problem when two different types of ink are ejected from two different sets of discharge nozzles, either in one print head, or in separate print heads. In such a device, cross-contamination of the different types of ink can occur on the respective discharge surfaces of the different sets of discharge nozzles. For example, black ink ejected from a black ink print head might inadvertently adhere to the discharge surface of a color ink print head during printing, thereby blocking the discharge nozzles of the color print head. In addition, inks of different types often react to result in a hardening of the combination ink on the discharge surface or, in the case of reaction inks, to quickly and strongly fix to the discharge surface, thereby impairing the operation of the respective discharge nozzles of the discharge surface.
For these reasons, ink jet printing devices often have the capability to perform some type of recovery of the discharge surface of the print head to maintain a good printing quality from the print head. For example, conventional ink jet printing devices often have a recovery system for performing recovery operations on the print head. Such a recovery system is often located in the main scanning direction of the carriage, but outside the printing area of the recording medium. Conventional recovery systems often include at least one cap which is shaped to engage and seal the print head, thereby protecting the discharge surface of the print head during non-use. In addition, a suction device, such as a purge pump, is often connected to the cap in order to remove undesirable contaminants from the discharge surface and the discharge nozzles of the print head while the cap is engaged to the print head. Furthermore, a typical recovery system also includes a wiper blade for wiping contaminants and adherents from the discharge surface and discharge nozzles of the print head. Often, a combination of these recovery operations is utilized to recover a printing quality of the print head. For example, the carriage on which the print head is mounted is first moved to the area of the recovery system. Then, the cap is engaged to the print head and negative pressure is applied by the suction device to draw contaminants, such as a residuary ink, from the discharge nozzles and discharge surface of the print head.
Optionally, a prefire operation may also be conducted in which the print head is commanded to eject a predetermined amount of ink in order to clear the discharge nozzles prior to printing. Such a prefire operation may take place while the cap is engaged to the print head, or may take place without having the cap engaged. Then, the cap is disengaged from the print head, after which the wiper blade is utilized to wipe the discharge surface of the print head. In this manner, the aforementioned recovery operations are utilized in an attempt to maintain the printing quality of the print head in as good a condition as possible.
While the conventional recovery system is used to remove contaminants and residual ink from the discharge surface and discharge nozzles of the print head, such recovery systems cannot sufficiently maintain a good printing condition of the print head in many situations. For example, in a conventional ink jet printing device with a recovery system as described above, it is often assumed that the print head is always positioned at a predetermined height above the recovery system during recovery operations. This predetermined height is desired to accommodate the length of the wiper blade, thereby ensuring consistent wiping of the discharge surface of the print head, as well as safe and consistent application of pressure from the wiper blade to the print head during wiping. In addition, the assumption of a predetermined height above the recovery system also facilitates the use of a known capping position in which to position the cap for effective engagement of the print head without causing damage to the print head.
In many instances, however, the actual distance between the print head and the recovery system varies due to a factory adjustment to account for position variations caused by the mechanical tolerance of each part. For example, a guide shaft which is provided to guide movement of the carriage in the printing direction is adjusted to satisfy a predetermined position of the carriage. In addition, the height of the carriage may be adjusted to account for a thickness of the recording medium during printing, thereby affecting the height of the carriage above the recovery system during recovery operations. Accordingly, when such conditions cause the gap between the print head and the recovery system to be inconsistent from one recovery operation to the next, the result of the wiping and capping operations will also be inconsistent.
A conventional recovery system may also be insufficient to maintain the print head in a good printing condition in the case where different inks are used in the ink jet printing device. If two different print heads are used which utilize two different types of ink, or if one print head is used which contains two sets of discharge nozzles which eject two different types of ink, problems can arise caused by cross-contamination of the two different types of ink on respective discharge surfaces. For example, when two different types of ink are utilized, such as dye and pigment inks, or reaction inks, it is preferable to use two separate caps wherein each cap is dedicated for capping of the set of discharge nozzles of each particular type of ink. In this manner, cross-contamination of ink on each cap is reduced during capping, thereby reducing subsequent cross-contamination from the cap to the respective discharge nozzles. However, during printing operation of the print head, each cap is left exposed and is therefore susceptible to cross-contamination by the adherence of ink which the cap is not intended to receive.
In addition, the caps are susceptible to contamination and damage from other sources, such as paper powder, dust and/or from improper handling by the user of the ink jet printing device. As discussed above, cross-contamination of the inks can cause the ink to fix on the cap, thereby reducing the ability of the cap to sufficiently form a seal on the print head. In addition, cross-contaminated ink residing on the cap can be transferred to the discharge surface of that cap's respective print head during capping operations, thereby contaminating the print head and impairing the printing condition of the discharge orifices of the print head.
The use of two different types of ink can also cause contamination of the wiper blade. Residuary ink particles are inadvertently distributed within the ink jet printing device during a printing operation and can adhere to the wiper blade while the wiper blade is not being used, thereby creating a cross-contamination of inks on the wiper blade. Such cross-contamination can reduce the effectiveness of the wiper blade during wiping of the discharge surface of the print head. In addition, a wiper blade which is cross-contaminated with two different kinds of ink can cause damage to a print head by contaminating the discharge surface of the print head with a different type of ink during a wiping operation. The wiper blade is also susceptible to other damage and contamination while the wiper blade is left exposed to the environment when not being used. The exposed wiper blade is therefore susceptible to other contaminants such as dust and paper powder, and is susceptible to damage from improper handling by the user of the ink jet recording device.
In addition to the above problems, the typical recovery system is often insufficient to remove residuary ink which is adhered to and dried on the discharge surface and discharge orifices of the print head. One possible solution is to perform a prefire operation to eject a limited amount of ink from the print head in an attempt to dissolve some of the dried residuary ink prior to wiping of the print head. However, if the prefire operation is performed near the recovery system, it may contaminate the cap, wiper and other parts with ink. It is also preferable to perform such a prefire operation away from the recording medium so as not to cause unwanted artifacts on the recorded image. One possible solution to such problems is to perform the prefiring at a location distant from the recovery system. In such a case, the time required to move the print head after prefiring to the location of the wiping blade for wiping can result in drying of the prefire ink prior to wiping, thereby reducing the effectiveness of the prefire operation.
In addition, if a separate prefire area is set aside in the scan direction of the carriage which is also outside the area of the recording medium and away from the recovery system, the size of the ink jet printing device is accordingly increased to accommodate the prefire area. Also, separate prefire areas are desired to receive the different types of ink when two different types of ink are used in a single print head, or in two separate print heads. Otherwise, cross-contamination of inks may occur within the ink jet printing device during prefiring which may impair the performance of parts affected by the contaminated ink.
A problem also occurs in conventional ink jet printing devices during capping of the print head when the cap is applied too quickly or forcefully to the print head. For example, if the cap is raised too quickly during the capping operation to engage the print head, or is applied to the print head with too much pressure, the cap can damage the discharge surface and discharge orifices of the print head. In addition, the foregoing conditions can result in the creation of positive pressure between the cap and the print head during the capping operation, thereby forcing air through the discharge nozzles, resulting in damage to the print head and the ink supply system by introducing air and air bubbles through the discharge nozzles into the print head.
Lastly, the use of two different types of ink in an ink jet printing device can cause cross-contamination of the respective sets of discharge nozzles, whether on one print head or on two separate print heads, when using a single wiper blade to wipe all discharge nozzles. For example, the use of a single wiper blade to wipe two different sets of discharge nozzles, each of which discharges a different type of ink, can result in the mixing of the two different inks on the single wiper blade which can cause cross-contamination and damage to the discharge orifices during subsequent wipings. In addition, if a print head is used which has an uneven print head surface, a single flat wiper blade cannot effectively wipe the discharge surface of the print head because the edge of the wiper blade will become distorted by the uneven discharge surface of the print head. In such a situation, the wiper blade will skip over areas of the discharge surface and will therefore be ineffective to clean residuary ink from the discharge surface.
In light of the problems with conventional recovery systems as discussed above, there is a need for an improvement in recovering the printing quality of the print head to a good condition.